I'm just new. so I would say "nice to meet you"

I've been trying to visualize D.I.C.E model with vensim but I am sticking about ZIDZ function. I have no idea what it is..
Have you ever used ZIDZ FUNCTION before and Would you like to explain in please?
The equation is
" interpolation fraction = max(0, zidz(45, 20)) "
45 and 20 are what I just put for looking simply.
Thanks
Have a great day
Jin
[Edited on 9-29-2010 by hoppang47]